Jumper cables are in common use for temporary connection of a charged storage battery in parallel with a weak or discharged battery. Many motorists carry such cables to enable "jump" starting of a car with a dead battery by using the charged battery of an adjacent vehicle. Once started, the generator or alternator provides sufficient energy to operate the vehicle and to recharge its depleted battery, and the jumper cables are disconnected.
The simplest form of a jumper-cable system is a pair of heavy (high-current) cables terminated at opposite ends in clamps for connecting the cables to terminal posts on the batteries. The problem with such simple systems is that it is both possible and easy to connect the batteries in reverse polarity which may damage one or both batteries, and even result in a hazardous battery explosion.
This problem has resulted in the availability of switch-protected jumper-cable systems which detect and signal correct (or incorrect) cable-battery connections before closing the circuit between the batteries. Signaling of a correct connection is typically done with simple pilot light and diode circuits, and switching by high-current devices such as automotive starter relays or massive plug-socket connectors as suggested in U.S. Pat. Nos. 4,166,241 and 4,272,142.
Some known jumper-cable systems are deficient or overly complex in assuring proper connections of correct polarity, and the starter-relay circuits present problems in that such relays are designed for only momentary activation during the cranking phrase of engine startup. These relays quickly overheat when used for jumper-cable switching of heavy starting currents, leading to short life and poor reliability.
The system of this invention overcomes these problems by providing accurate polarity determination, and by eliminating the commonly used starter relays which are susceptible to overheating and failure. Broadly, the new system is an optimized combination of electrical circuitry for polarity sensing, and a pair of latched heavy-duty mechanical switches which readily withstand heavy current without overheating. The polarity-sensing circuitry unlatches only one of the switches to insure correct interconnection of the batteries, and that switch is then manually actuated to complete the connection. The system is simple for an inexperienced person to operate, and is primarily intended for permanent installation in the user's automobile, either as original equipment, or as a subsequently installed accessory.